1. Technical Field of the Invention
The present invention particularly relates to a liquid detecting device which is suitable for detecting a residual amount of a liquid (ink) in a liquid ejecting apparatus such as a recording apparatus of an ink jet type, a liquid container including the same device, and a method of manufacturing the liquid detecting device.
2. Description of the Related Art
Typical examples of a conventional liquid ejecting apparatus include a recording apparatus of an ink jet type which comprises a recoding head of an ink jet type for recording an image. Examples of other liquid ejecting apparatuses include an apparatus comprising a coloring material ejecting head to be used for manufacturing a color filter of a liquid crystal display, an apparatus comprising an electrode material (conducting paste) ejecting head to be used for forming an electrode of an organic EL display or a surface emitting display (FED), an apparatus comprising a bioorganism ejecting head to be used for manufacturing a biochip, and an apparatus comprising a sample ejecting head to be a precision pipette.
The recording apparatus of the ink jet type according to the typical example of the liquid ejecting apparatus has such a structure that an ink jet recording head having pressure generating means for pressurizing a pressure generating chamber and a nozzle opening for ejecting a pressurized ink as an ink droplet is mounted on a carriage and the ink in an ink container is consecutively supplied to the recording head through a passage, and printing can be thus carried out continuously. The ink container is constituted as a detachable cartridge which can easily be exchanged by a user when the ink is consumed, for example.
Conventionally, a method of managing the consumption of the ink by the ink cartridge includes a method of integrating, in software, the number of ejections of the ink droplet by the recording head or an amount of the ink sucked for a maintenance to manage the consumption of the ink by a calculation and a method of attaching an electrode for detecting a liquid level to the ink cartridge, thereby managing a time that the ink is actually consumed in a predetermined amount.
However, the method of integrating, in software, the number of ejections of the ink droplet or the amount of the ink to manage the consumption of the ink by a calculation has the following drawback. Some heads have a variation in a weight of the ejected ink droplet. The variation in the weight of the ink droplet does not influence picture quality and the ink cartridge is filled with the ink in an amount having a margin in consideration of the case in which an error of the amount of the consumption of the ink which is made by the variation is accumulated. Accordingly, there is a problem in that the ink is left corresponding to a margin depending on an individual.
On the other hand, the method of managing the time that the ink is consumed by the electrode can detect the actual amount of the ink. Therefore, the residual amount of the ink can be managed with a high reliability. However, the detection of the liquid level of the ink depends on a conductivity of the ink. For this reason, there is a drawback that the type of the ink which can be detected is restricted and a seal structure of the electrode is complicated. Moreover, a noble metal having a high conductivity and a high corrosion resistance is usually used as a material of the electrode. Consequently, a cost for manufacturing the ink cartridge is increased. Furthermore, it is necessary to attach two electrodes. Therefore, a manufacturing process is increased. As a result, the manufacturing cost is increased.
Therefore, an apparatus developed to solve the problems has been disclosed as a piezoelectric device (referred to as a sensor unit or a liquid detecting device) in JP-A-2001-146024. The sensor unit serves to monitor the residual amount of the ink in the ink cartridge by utilizing the fact that a resonant frequency of a residual oscillation signal caused by a residual oscillation (free oscillation) of an vibration plate after a forced oscillation is varied in the case in which an ink is present or is not present in a cavity opposed to the vibration plate in which a piezoelectric element is laminated.
In the case in which the sensor unit described in JP-A-2001-146024 is used, it is necessary to cause the ink to freely enter the cavity opposed to the vibration plate. However, it is necessary to prevent the ink from entering a side on which a piezoelectric unit to be an electrical element is disposed. For this reason, different members should be sealed strictly.
As sealing structure for sealing the sensor unit and the container body, there is known a structure that the sensor unit is bonded directly to the circumferential edge of an opening of the container body or a structure that the sensor unit is bonded directly to the circumferential edge of an opening of a module and then the module is mounted on the container body with an O ring therebetween. However, since the sensor unit is bonded to the circumferential edge of the opening, deviation in size makes it difficult to secure the sealing ability. In addition, when the sensor unit is bonded directly to the circumferential edge of the opening of the container body or the circumferential edge of the opening of the module, it can be easily affected by a wave motion of the ink or bubbles in the ink, thereby causing erroneous detection.
Furthermore, seal means for sealing the different members in the sensor unit includes means for giving a breaking margin, thereby sealing a clearance by a surface pressure, for example, an O ring. In the seal means such as the O ring, a sealing performance depends on precision in the dimensions of a plurality of components. For this reason, there is a problem in that a mass production is hard to stabilize. Moreover, a component for breaking the O ring is required separately. Consequently, there is also a problem in that a size of a sensor unit (a liquid detecting device) is increased.
As another seal means, moreover, it can be proposed to seal a clearance between components with an adhesive. In the case in which the adhesive is used, there is a problem in that handling is troublesome and a stabilization of a process in the mass production is hard to implement. In the case in which a plurality of components formed of different materials (for example, ceramics, metals or resins) is combined to fabricate the sensor unit (the liquid detecting device) in order to enhance oscillating characteristics, particularly, it is hard to select the adhesive and it is also demanded that a place for using the adhesive should be limited as greatly as possible.